package mao.exaimnation.jd;

import java.util.Scanner;

/**
 * @author Totoro
 * @date 2020/8/6
 * @explain:
 */
public class Main1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double result=0;
        while (scanner.hasNext()){
            result=0;
            int n = scanner.nextInt();
            for (int i = 1; i <= n; i++) {
                //注意类型转换。
                result+=((double) 1)/(5*(2*i-1))-((double) 1)/(5*2*i);
            }
            //输出表达式
            System.out.format("%.4g",Math.round(result*10000)/(double)10000);
        }
    }
}
